Antifading device



Sept. 25, 1934.` RgvlLLEM r-:r AL

ANTIFADING DEVICE Filed Jan. A16, 1950 lNvENToRS' RAYMOND `VILLEM mo BY Rom Auen 7l 77 ATTORNEY Patented Sept. 25, 1934 PATENT trice ANTIFADING DEVICE Raymond Villem and Roger France, assignors to Aubert, Paris, Compagnie Generale de Tclegrapnie Sans Fil, a corporation of France Application January 16 1930, Serial No. 421,079

In France January 26, 1929 3 Claims.

The present invention has as its object, improvements in devices used to eliminate the effect of fading; or to prevent the disappearance of signals transmitted through space by electromagnetic waves.

There are known to the prior art various arrangements by means of which, in an amplifying receiver, the sensitiveness of one or more of the amplifying elements is varied in indirect proportion to the intensity of the signal in the manner such that, at the time of extreme fading, the amplification is at its maximum, while it is materially decreased during a period of strong signals. i

This regulation is generally obtained by the automatic variation of the polarization or biasing of the grids of amplifying tubes. This operating method, while serving the purpose, is accompanied by the disadvantage that it introduces a detector action in the amplifying elements, which is particularly objectionable due to the deformations or distortion which it produces.

The present invention concerns a method of regulation which avoids this inconvenience. It consists essentially in providing the coupling of an aniplier tube with the next one by means of the placing of a compound resistance in the plate circuit, this resistance comprising, in parallel an ohmic resistance and the inner cathode resistance of an emission tube or electron discharge device. The intensity variations of the received current, after suitable transformation, usually by means of so-called direct current amplifiers, act upon the control electrode of the tube, thereby modifying at will its inner resistance and, consequently the coefficient of amplification of the stage.

The inventionmay be better understood by means of the attached drawing which shows by way of example only, an embodiment and a method of utilization of the present invention. Fig. 1 represents the device which effects the particular object of this invention While Fig. 2 shows a method of application of this device to a receiving set.

According to Fig. 1 an amplification stage is builtin the following manner: The amplifier tube 1 is supplied with oscillations at 2 and transmits to output circuit 3 the amplified oscillations. The anodes of tubes 1 and 5 are connected with the plate supply (HT) through an interposed single or compound impedance 4 (purely ohmic resistance, or inductance, plug circuit, etc.). In syntony with this impedance 4 (by means of sources not shown) is provided the inner resistance of a multiple electrode tube 5. The potential of the grid of this tube is varied by means of the current owing through resistance' 6 of current coming from conductors 7, selected for instance, from signalling currents after the final detection and suitably converted to direct current and transformed to a sunicient value.

The variations of this regulating current, there.'- fore, follow those of the carrier wave produced by the fading in the manner that, in a period of extreme fading, the internal resistance of tube 5 is as large as possible and, in consequence, the amplifying action of the stage at its maximum, while in a period of loud signals, the resistance of tube 5 decreases and, therefore, the amplification of the stage decreases. This action may even be rendered more pronounced by the interposition of a resistance 8 between the plate of tube 5 and the impedance 4. It should be understood that, while a triode tube has been described by way of example, the invention may make use of other types of tubes, such as tubes containing two grids, tubes with a plate-screen, multiple electrode tubes, etc.) It may also take the form of a symmetric set by means of the duplication of its elements.

Fig. 2 represents the application of the invention to an amplifying receiver of the variable frequency type, the invention making use of the device as one of the amplification stages of intermediate frequency. In the figure may be seen the tubes 1 and 5, the impedance 4, resstances 6 and 8; the receiving current enters after having been collected upon antenna 20', amplified at radio frequency amplifier 22, and heterodyned in a modulator or atrZ, frequency changer 24.

Another tube 9 may follow the device, described in Fig. l of the invention, containing a selective coupling element such as the oscillating or tunable circuit 10. vAfter passing through this element the received heterodyned current is parted in two ways: one, into arnplier 11, detector 12, audio frequency amplier 30 and utilization element 32 which may be a telephone receiver, recorder, etc.; the other, by way of amplifier 13, which collects the tuned current, detector 14 which rectifies it, amplifiers 15, 16, 17, 18 acting as direct current amplifiers, causing current variations in the resistance 6, thereby causing the variation of the grid potential of tube 5, as has been explained. Y

Into the plate circuit of one of the last ampliners, for instance 17,l a circuit of very great time constancy 19 is introduced which is produced by connecting in parallel a large capacity condenser and a resistance of high resistance. For the sake of clarity, the source and the heating current for the filaments are not shown, except that 20 represents the divers points related to this heating circuit. The plate supply, supposed to be the same for all tubes, is shown in 21.

It is Well understood that the invention is sub- `ect to a number of modifications as to embodiments as well as applications, especially with respect to the type of tubes employed, also with respect to the location of the device, which is the object of the invention, with regard to the dierent stages of an amplifying receiver (before or after the change in frequency, radio frequency amplications or intermediate or audio frequency amplication) and nally with respect to the method employed in producing the variations of the direct current.

What is claimed is:

1. In a superhetercdyne receiver arrangement for receiving electric currents, intermediate frequency amplier means comprising a coupling element comprising an impedance shunted by the resistance between two electrodes of a multielectrode tube, means coupled to the second detector input for detecting received currents, and means for varying the polarization of said tube by the detected currents, said last mentioned means comprising in the control electrode circuit of said tube a resistance, a cascade amplifier fed with the detected current for passing direct current through said resistance, whereby an increase in the said currents correspond to a reduction of the incoming current, and vice versa. 2. In an arrangement for receiving electric currents, radio frequency ampliiier means comprising a coupling element comprising an impedance shunted by the resistance between two electrodes of a multi-electrode tube, means for detecting the received currents, means for controlling the said internal resistance by the detected currents, the latter currents being of such a magnitude that the sense of variation of the said resistanceis inverse to that of the variation of the incoming current, and another impedance between the plate of the tube whose resistance is varied, and the plate of the radio frequency arnplication stage preceding said coupling element. 3. In a receiving system, an electron discharge device high frequency ampliiier, a resistance in the output circuit of said ampiier, means for detesting a portion. of the output of said ampliiier, means for amplifying the detected portion, an electron discharge device connected across said resistance so that its internal impedance shunts said resistance, and means for applying the detected and amplified portion to the control electrodes of said shunting electron discharge device whereby the effective resistance of said resistance in the output circuit oi said amplifying electron discharge device is varied inversely to the strength of received high :frequency energy.

RAYMGND VILLEM. ROGER AUBERT. 

